The present invention relates to an intake manifold for an internal combustion engine.
The intake manifold of an internal combustion engine defines a flow path between a throttle valve and each cylinder of the engine. In an intake manifold of a certain type, there are two separate, parallel flow passages in the flow path downstream from the throttle valve, and the air flow passing through the throttle valve may be divided between the two flow passages under certain operating conditions. The two flow passages converge in the flow path before the flow path reaches the cylinder. The first of the two flow passages includes a long runner plenum and a long runner for each cylinder, and the second flow passage includes a short runner plenum and short runners a short runner for each cylinder. The purpose of the long and short runners is to improve the volumetric efficiency of the engine at both high and low engine speed ranges.
In operation, the air flow into the cylinders of the engine is controlled by adjusting the opening of the throttle valve. The air passing through the throttle valve may be divided between the two flow passages. At a low engine speed, the short runners are blocked, and the intake air passes through the long runner plenum and the long runners to reach the cylinders. At a high engine speed, the short runners are unblocked, and the intake air flows through the short runner plenum and the short runners, as well as the long runner plenum and the long runners, to reach the cylinders. The air flows from the long and short runners for each cylinder converge before the air flow reaches the cylinder.
U.S. Pat. No. 5,632,239 describes an example of the conventional intake manifold for a V-6 engine. FIGS. 1 and 2 of the patent show a three-plenum air distributing manifold 10. Referring to FIG. 2 of the patent, the manifold 10 has a long runner plenum 22, 24 for each bank of cylinders, and all cylinders share a short runner plenum 14 disposed between the long runner plenums 22, 24. The long runner plenums 22 and 24 are connected to one another at one end of the manifold 10 adjacent the throttle body 16 by transversely extending zip tubes 28 and 30. The long runner plenums 22, 24 are also connected to one another at an opposite end of the manifold 10 by a laterally extending crossover passage 34. The flow through the cross over passage 34 is regulated by a manifold tuning valve 42 which is mounted at a mid-position in crossover passage 34. The MTV 42 has a valve plate 43 which is selectively pivoted between opened and closed positions by an actuator.
As shown in FIG. 1, the left side long runner plenum 22 is connected to the three cylinders in the right hand cylinder bank of the engine 12 by long runners 50, 52 and 54. As shown in FIGS. 1 and 3, the right side long runner plenum 24 is connected to the three cylinders of the left hand bank by long runners 64, 66 and 68.
Referring now to FIGS. 3 and 4, the manifold 10 has six short runners 80, 82, 84, 86, 88 and 90 connecting the short runner plenum 14 to the six cylinders, respectively.
The air flow through each of the short runners is controlled by closing or opening a short runner valve 96 as best seen in FIGS. 3 and 4 ( ). In the closed position of the short runner valve 96, air flow through the short runners 80-90 is blocked. Resultantly, air flow to the engine cylinders is through the throttle body 18, zip tubes 28, 30, long runner plenums 22, 24, and long runners 80, 82, 84, 86, 88, and 90, before the intake air enters the cylinders. This operative mode for the intake system is advantageous for idle and low speed operation of the engine.
The engine performance over a relatively high speed range, such as a wide open throttle condition, is enhanced by directing air flow from the short runner plenum 14 and through the short runners 80, 82, 84, 86, 88, and 90. This is accomplished by opening the short runner valves 96. The intake air flows directly from the short runner plenum 14, through the short runners 80, 82, 84, 86, 88, and 90, and into the engine cylinders.
The conventional intake manifold has a number of problems. For example, when the engine speed is low and the short runners are blocked, various residual gases are collected in the short runner plenum. The residual gases include exhaust gas recirculation (EGR) gas, fuel tank purge vapor, and positive crankcase ventilation gas. When the throttle valve is closed or near the closed position, such as during deceleration of the vehicle, the residual gases stored in the short runner plenum are sucked into the cylinders via the long runner plenum and long runners, and must be compensated for by the engine control system. This increases the difficulties of controlling the engine and reduces the accuracy of engine control.
In addition, the conventional intake manifold has poor mixing of EGR gas with the intake air. The exhaust gases for each cylinder bank are introduced to the intake air either separately (one EGR entry point for each cylinder bank) or they enter at a point very close to the point where the manifold splits the air flow between the cylinder banks. As a result, the length of the flow path is not long enough to achieve sufficient mixing of the EGR gas with the intake air.
Further, the conventional intake manifold, such as the one shown in FIG. 2 of U.S. Pat. No. 5,632,239, is so wide that it is difficult to mount the engine transversely in the engine compartment of the vehicle, because the conventional intake manifold must be wide enough to accommodate the width of the two long runner plenums and the length of two sets of long runners.
The present invention overcomes some of the problems associated with the conventional intake manifold by providing an intake manifold for a V-type engine having first and second banks of cylinders, wherein the intake manifold includes an air inlet for admitting air into the manifold, a first plenum in fluid communication with the air inlet, and second and third plenums that are each in fluid communication with the first plenum. The intake manifold includes a short runner for each cylinder of the engine, which short runner connects the first plenum to the cylinder. The intake manifold further includes two sets of long runners. Each long runner of the first set connects the second plenum to a cylinder of the first cylinder bank, and each long runner of the second set connects the third plenum to a cylinder of the second cylinder bank.
In low speed engine operation, the short runners are closed, and the intake air enters the manifold through the air inlet, passes through the first plenum and then through the second and third plenums, and passes through the long runners, before the intake air reaches the cylinders.
In high speed operation, the short runners are open. In addition to the air flow passing through the long runners, a large portion of the intake air passes through the short runners to reach the cylinders. The air flows passing through the long and short runners converge before the intake air reaches the cylinders.
In accordance with another aspect of the invention, an intake manifold includes an air inlet for admitting air into the manifold, and first, second and third plenums each in fluid communication with the air inlet, wherein the second and third plenums are substantially vertically aligned and preferably are placed on one side of the first plenum. The intake manifold includes a short runner for each cylinder of the engine, which short runner connects the first plenum to the cylinder. The intake manifold further includes two sets of long runners. Each long runner of the first set connects the second plenum to a cylinder of the first cylinder bank, and each long runner of the second set connects the third plenum to a cylinder of the second cylinder bank.
The second and third plenums, i.e. the long runner plenums, may be connected through a manifold tuning valve. The manifold tuning valve is closed during wide open throttle and/or low-vacuum (i.e. high engine load) conditions at the lower range of engine speeds. The closed valve causes acoustic pressure waves generated in each of the long runner plenums to return to the interior of the plenum and constructively act upon the pulsed air flow caused by opening and closing of the engine intake valves. As a result, the air flow through the long runners is enhanced to improve the engine""s volumetric efficiency and torque.
The present invention has a number of advantages over the conventional intake manifold. For example, in accordance with one aspect of the invention, the first plenum connected to the short runners is no longer a deadend when the short runners are closed. When the short runners are closed, the air passes through the first plenum on its way to the second and third plenums connected to the long runners. Consequently, even when the short runners are closed, there are no residual gases collecting in the first plenum.
In addition, the distribution and mixing of gases (i.e. EGR gas, fuel tank purge vapor, and positive crankcase ventilation gas) with the intake air may be improved in the present invention, because the mixing length and time can be increased due to the increased length of air flow to the long runners. The air flow to the long runners may pass through not only the long runner plenums but also the short runner plenum. This assures a more homogenous mixture of introduced gases and intake air, and reduces cylinder-to-cylinder variation in fuel/air ratio.
Further, the intake manifold of the present invention may be narrower than the conventional intake manifold, so that the engine can be relatively easily mounted transversely in the engine compartment of the vehicle. The intake manifold of the present invention may be narrower because the long runner plenums may be stacked vertically on top of each other on one side of the short runner plenum. In the conventional manifold, on the other hand, the long runner plenums are spread out horizontally on both sides of the short runner plenum.
Still further, because the long runner plenums may be vertically stacked and the distance between the two plenums may be small, the passage between the long runner plenums can be short. As a result, the energy-loss from the pressure waves which travel between the two long runner plenums for the purpose of manifold tuning is reduced, resulting in greater tuning efficiency. In a conventional design, on the other hand, each long runner plenum is positioned over a cylinder bank, and the passage between the two plenums is a long tube or duct. The length and volume of this tube or duct increases the energy-loss of the pressure waves, resulting in low tuning efficiency.